Preparation of aromatic amines



United States Patent M PREPARATION OF AROMATIC AMINES Charles L. Thomas,Swarthmore, Pa., assignor to Sun Oil Company, Philadelphia, Pa., acorporation of New ersey No Drawing. Application November 5, 1953,

Serial No. 390,409

3 Claims. (Cl. 204-168) This invention relates to the preparation ofamino derivatives of aromatic hydrocarbons, and specifically relates tothe preparation of aromatic amines of the benzene series.

Methods heretofore described for the preparation of aromatic aminesgenerally involve multi-step processes wherein an aromatic hydrocarbonis converted to a derivative which in turn is converted to the amine.For example, benzene is converted to nitrobenzene which is then reducedto aniline, or benzene is converted to chlorobenzene which is thenreacted with ammonia to produce aniline. Due to the several reactionsrequired by such multi-step processes, the apparatus employed iscomplicated and the technique of operation diflicult. Corrosive reagentsare required, which necessitate special and expensive materials ofconstruction, and frequently present a disposal problem of wastematerials.

An object of the present invention is to provide a process for thepreparation of aromatic amines from benzene hydrocarbons in a singlestep. A further object is to provide a commercially feasible process forthe direct conversion of an aromatic hydrocarbon to an amine. Anotherobject is to provide a process for the preparation of aromatic amineswhich does not require complicated apparatus of special materials ofconstruction. A still further object is to eliminate the need forcorrosive reagents in the production of aromatic amines. Other objectswill be apparent from the following specification.

It has now been found that by passing a mixture of an aromatichydrocarbon and ammonia through a non-disruptive electric discharge, thearomatic hydrocarbon and ammonia react to form hydrogen and the aminoderivative of the aromatic hydrocarbon.

In a specific embodiment of the process of the invention, a mixturecontaining benzene and ammonia is passed, in vapor phase, through anelectric glow discharge. Aniline and hydrogen are the products recoveredfrom the efliuent mixture. The process of the invention thus provides asingle step process for the production of aromatic amines in which theneed for complicated apparatus constructed of special materials,difiicult operational techniques and corrosive reagents is eliminated.Although the mechanism of the reaction is not known with certainty, theoverall reaction can be represented by the equation:

By the term, non-disruptive electric discharge," and terms of similarimport as used herein, is meant the types of electric discharge whereinvisible arcing or sparking between electrodes it at least substantiallyprevented, and which are known to produce ozone from oxygen. Silentelectric discharges, corona discharges and brush discharges illustratesuitable non-disruptive discharges which can be employed. Such nondisruptive electric discharges are obtained by using an alternatingcurrent po- 2,749,298 Patented June 5, 1956 tcntial having a frequencyof from about 50 cycles per second to 10,000 kilocycles per second atvoltages of from about 500 to 30,000 volts. Best results are obtainedwith what may be termed a true silent electrical discharge used in anapparatus such as an ozonator, i. e., apparatus used to convert oxygento ozone. In ozonators, the electrodes are separated by an insulator toprevent arcing. The electrodes collect charges of ions during /2 cycleof the alternating current and release them when the polarity reverses.Non-disruptive discharges operate at relatively high temperatures sothat cooling means are preferably employed for adjacent portions of theapparatus.

Aromatic hydrocarbons which can be employed in the process of theinvention are those of the benzene series which have at least onereplaceable hydrogen atom attached to a carbon atom of the aromaticnucleus. Benzene, toluene, ethylbenzene, n-propylbenzene,isopropylbenzene, ortho-xylene, meta-xylene, para-xylene, 1,2,3-trimethylbenzene, 1,2,4 trimethylbenzene, 1,2 diethylbenzene,2-ethyltoluene, and normal butyl benzene illustrate the aromatichydrocarbons which give good results. The aromatic hydrocarbon must nothave more than 5 alkyl substitutents and preferably does not have morethan 4 alkyl substituents. It is also preferred that the alkylsubstituents attached to the aromatic nucleus should have not more thanabout 5 carbon atoms, since higher alkyl substituents tend to cleave inthe process.

It is preferred to supply a mixture of aromatic hydrocarbon and ammoniato the non-disruptive discharge in vapor phase, but liquid phaseoperation can be employed if desired. Pressures of from about 5millimeters of mercury absolute pressure up to about 100 p. s. i. can beemployed. In general, the pressure is adjusted to give maximumelectrical eificiency. The time the reactants are subjected to thedischarge is adjusted to secure an eificient conversion of the aromaticto the amino derivative, and will usually be from a fraction of asecond, say about 0.01 second, to about 1 minute. The pressure andtemperature employed can be such that the aromatic hydrocarbon is inliquid phase and the ammonia in vapor phase, in which case suificientammonia is in intimate contact with the aromatic hydrocarbon,particularly at relatively high pressure, to secure good results in theoperation. The temperature of the mixture supplied to the glow dischargeis preferably at a temperature of from about 10 C. to 200 C.

The ratio of reactants to employ can be varied substantially and goodresults obtained therewith. It is preferred to employ a mole ratio ofaromatic hydrocarbon to ammonia of from about 0.1 :1 to 20: 1.

To illustrate a specific embodiment of the process, benzene is vaporizedand admixed, at a rate of about 36.8 pounds per hour, with vaporizedammonia, the mole ratio of benzene to ammonia being maintained at about2:1. The resulting mixture, in vapor phase at a temperature of about C.,is passed at atmospheric pressure through a silent electric discharge.Hydrogen and unreacted ammonia are removed from the eifiuent reactionstream. The remaining products, aniline and unreacted benzene, areseparated, aniline being recovered at a rate of about 2 pounds per hour.The recovered benzene is advantageously recycled to the process.

When other aromatic hydrocarbons are substituted for benzene, the aminoderivatives thereof are produced in the process with substantiallyequivalent results. For example, toluidine is prepared from toluene andxylidine is prepared from xylene, it being understood that the productsin such instances consist of a mixture of isomers.

Another embodiment of the process is the substitution of actinic lightfor the non-disruptive electric discharge. in this embodiment a mixtureof an aromatic hydrocarbon and ammonia is subjected to irradiation sothat the aromatic hydrocarbon, ammonia, or both, is activated. Reactionbetween the ammonia and aromatic hydrocarbon then occurs to formhydrogen and the amino derivative of the aromatic hydrocarbon. Byactinic light" is meant irradiations generally in the ultraviolet rangehaving a wave length from about 5000 to about 1000 angstrom units. Thesource of actinic light is preferably a mercury are operated in a fusedsilica tube, but other sources such as rare-gas lamps and enclosedcarbon-flame arcs can be employed with good results. Such sources ofultraviolet light are preferably operated in apparatus constructed offused silica, special phosphate glasses, crystal quartz, or lithiumfluoride, de pending upon the Wave length of the ultraviolet lightdesired. In operating the process, it is important that both thearomatic hydrocarbon and ammonia be maintained in the gas phase duringexposure to the actinic light.

If desired, two sources of actinic light supplying irradiations ofdill'erent wave lengths into a single reaction chamber may be employed,one wave length being espccially suitable for the dissociation ofammonia and the other Wave length being especially suitable for thedissociation of the aromatic hydrocarbon into a hydrogen atom and anaryl radical. A still further embodiment is to expose separately streamsof ammonia and aromatic hydrocarbon to actinic light and to combine thestreams from the exposure chambers immediately thereafter, so that theactivated materials are brought into immediate contact.

In this embodiment, as for the non-disruptive electric dischargeembodiment, aniline, toluidine, and xylidine are prepared from benzene,toluene, and xylene, respectively, it again being understood that theproducts in some instances consist of a mixture of isomers.

The invention claimed is:

1. Process for the preparation of aromatic amino hydrocarbons whichcomprises forming a liquid phase mixture of an aromatic hydrocarbonhaving a replaceable hydrogen atom attached to the aromatic nucleus withammonia, the mole ratio of said aromatic hydrocarbon to ammonia beingfrom 0.121 to 20:1, passing the mixture through a non-disruptiveelectric glow discharge, and recovering an aromatic amino hydrocarbonfrom the reaction mixture.

2. Process according to claim 1 wherein said aromatic hydrocarbon havinga replaceable hydrogen atom attached to the aromatic nucleus is benzene.

3. Process according to claim l wherein said aromatic hydrocarbon havinga replaceable hydrogen atom attached to the aromatic nucleus is toluene.

References Cited in the file of this patent UNITED STATES PATENTS1,307,931 Schmidt et al. June 24, 1919 1,994,243 Eglott et al. Mar. 12,1935 2,334,377 Bennett Nov. 16, l943

1. A PROCESS FOR PREPARATION OF AROMATIC AMINO HYDROCARBONS WHICHCOMPRISES FORMING A LIQUID PHASE MIXTURE OF AN AROMATIC HYDROCARBONHAVING A REPLACEABLE HYDROGEN ATOM ATTACHED TO THE AROMATIC NUCLEUS WITHAMMONIA, THE MOLE RATIO OF AROMATIC HYDROCARBON TO AMMONIA BEING FROM0.1:1 TO 20:1, PASSING THE MIXTURE THROUGH A NON-DISRUPTIVE ELECTRICGLOW DISCHARGE, AND RECOVERING AN AROMATIC AMINO HYDROCARBON FROM THEREACTION MIXTURE.